This health services research study will analyze existing data from a sample of states and the National Household Survey on Drug Abuse to understand, measure, and describe substance abuse treatment need in the US. Treatment need plays a central role in understanding many substance abuse services research issues, including resource allocation, treatment utilization, managed care, racial disparities, the national treatment gap, diversion of abusers from jail to treatment, and office-based methadone treatment. However, there is no well-developed and validated measure of treatment need. Having a substance-use disorder diagnosis is the most commonly used indicator of treatment need, but many people who receive treatment do not have a diagnosis, and most people in the general population who have a diagnosis do not receive or want treatment. Leading scholars who originally developed survey-based diagnostic scales have recently argued that diagnosis and treatment need are not equal and should be measured differently, and they believe that additional research is required to arrive at a satisfactory measure of treatment need. The proposed study will develop a standardized measure of treatment need using existing survey data designed for this purpose and will cross-validate the measure on a series of diverse state surveys and the NHSDA. The state surveys included adult and adolescent household and nonhousehold samples (prisoner, homeless, and treatment client). The survey questionnaire contained the DIS, questions on treatment history, and other measures that reflect the concept of treatment need. The proposed study will analyze the data to test the theoretical analysis of treatment need presented in the proposal, construct a composite measure of need, and assess the construct validity of the need scale. A version of the scale will be applied to 2000-2002 NHSDA data, and the study will estimate the current national treatment gap.